Field of the Invention
The present invention relates to a toner for developing an electrostatic image to be used in image-forming methods, such as electrophotography and electrostatic printing.
Description of the Related Art
A typical apparatus of an electrophotographic system that uses a toner is, for example, a laser printer or a copying machine. In recent years, the colorization of such apparatus has rapidly advanced, and hence a further improvement in image quality has been required. Accordingly, various investigations have been made with a view to achieving the control of chargeability and flowability for obtaining stably high image quality.
In Japanese Patent Application Laid-Open No. 2014-142605, there is a disclosure of a technology involving externally adding silica particles each having a specific carbon content and composite oxide particles to toner particles to suppress a reduction in chargeability of a toner.
In addition, in recent years, the following design has been made. The amount of a toner to be loaded into a cartridge is reduced to the extent possible so that the toner may be used up at the time point of the exchange of the cartridge. In such design, at the timing at which the exchange of the cartridge is drawing near, the frequency at which the following cycle is repeated increases. The particles of one and the same toner are subjected to development, return to the cartridge without being developed, and subjected to development again. Thus, the toner repeatedly receives a mechanical stress. Accordingly, the toner is required to have higher development durability. When a reduction in charge quantity or flowability of the toner occurs in a state in which the amount of the toner in the toner cartridge is small, it becomes difficult to obtain a satisfactory solid image.
In such approach as disclosed in Japanese Patent Application Laid-Open No. 2014-142605 involving causing the fine particles to adhere to the surfaces of the toner particles to improve various kinds of performance, the deviation, embedment, or the like of the fine particles occurs as the toner is repeatedly used for a long time period. Accordingly, when the toner undergoes such cycle as described above, it becomes difficult to maintain desired chargeability and flowability thereof at high levels.
In view of the foregoing, in Japanese Patent Application Laid-Open No. 2010-181439, there is a proposal of a technology for an improvement in development durability. In Japanese Patent Application Laid-Open No. 2010-181439, an attempt to improve the development durability is made by: causing a silicon compound containing an ethylenically unsaturated bond to react with a toner to cover the surfaces of the particles of the toner; and externally adding inorganic particles from above the covered surfaces to improve the charging stability of the toner. However, an influence of the embedment of the inorganic particles cannot be ignored, and hence the development durability is still susceptible to improvement.